MILES AND GRINNELL GLACIERS 419
glacier was very marked. To the left of the second rapid the river had cut out the bowlders and worn a huge hole in the glacier,1 some 50 or 60 acres in area, which is the entering wedge for the formation of a new channel. The face of Miles Glacier below the fourth rapid, has receded some 5 or 6 miles to the east, or back from the river, and during the months of June, July, and August, the falling of bergs cut out by the comparatively warm river water from tfaig glacier keep up a continual roar, as they fall off."
Corporal Koehler states that "during October tons and tons of ice broke off Miles Glacier which caused a noise like thunder and made the swells of the river almost reach the camp. In the morning the bay was found to be blocked by ice. Only to the extreme right was there an opening sufficient through which to navigate the boat." Guide Rafferty indicates that Miles Glacier was much the same in July as in October, 1898.
By October, 1900, the southern half of Miles Glacier seems to have retreated still farther, the ice cliff photographed by Schrader and Spencer and mapped by Wither-spoon being farther back at least than in Hayes' sketch map of 1891, and the lake being larger.8 This map does not represent as ice the stagnant northern portion of the glacier which causes Abercrombie Rapids, showing only a narrow distributary ice tongue north of the main glacier, doubtless where there was clear ice visible. Earlier observations prove that ice must have underlain this whole moraine-covered belt in 1900. A. C. Spencer has stated3 that marked recession of Miles Glacier took place between 1899 and 1900.
In August, 1905, the Miles Glacier was photographed by Webster Brown, and in October, 1907, by F. H. Moffit, of the U. S. Geological Survey. The photographs by Moffit show that one lobe of the ice front terminating in the lake retreated approximately 1700 feet between 1900 and 1907, by comparison with the Schrader and Spencer photographs.
Observations by the Railway Engineers. The railway and bridge engineers of the Copper River and Northwestern Railway surveyed their right of way west of Miles Glacier and built their great steel bridge and the railway between 1906 and 1910, mapping the cliff of Miles Glacier, the lake and its outlet, and the Abercrombie Rapids. Their maps show marked enlargement of the lake between 1900 and 1908, with a slight recession on the south side of the glacier so that the middle projects in a pronounced point. A later map shows advance of the glacier and decrease in width of the lake.
The railway engineers made soundings in the lake, measured the Velocity of the stream at the outlet of the lake, determined the rate of iceberg flow, bored through the glacial deposits near the bridge, kept a detailed meteorological record for three years, and made many general observations, from their camp between Childs and Miles Glaciers, where they were building the steel bridge across Copper River and operating a car ferry across the Miles Glacier lake in 1909 and 1910. Many excellent photographs of Miles Glacier were also taken by individual engineers, and by E. A. Hegg, of Cordova.
* The Bearhole.
»Geology and Mineral Resources of a Portion of the Copper River District, House Doc. 546, 56tib Congress, 2nd Session, Washington, 1900, Fl. "STTT B, and map, PI. II; also reproduced as PL XII, in Bull. 284, U. S. Geol. Survey, 1906. A later edition of Witherspoon's map of Miles Glacier, with slight modifications, including the widening of the lake through the retreat of the ice front, has also been published by the IT. S. Geol. Survey, Bull. 874, 1909, PI. I.
• In H. P. Reid's Variations of Glaciers, Journ. Geol. Vol. IX, 1901, p. 253.